Vulnerable children could be left at risk because new Government migrant limits have made it even more difficult to fill social worker vacancies, it was claimed today.

Moves by Ministers to cut the number of skilled workers coming to the UK from outside the EU this year by 5% have hit recruitment of child protection officers, according to recruitment agency The Synergy Group.

But the Government said social work with children and families was recognised as a "shortage occupation", meaning employers can seek extra permits for foreign workers to fill vacancies.

A recent survey discovered one in seven social worker posts was empty as councils struggled to find suitable candidates after the Baby Peter tragedy.

The Synergy Group estimated 3,000 child protection roles could be unfilled across England - potentially leaving as many as 45,000 at-risk youngsters without an officer allocated to look after them.

Richard Evans, the company's international recruitment manager, said recruiting overseas social workers was an effective solution to the shortage of candidates in this country.

But he added: "The harsh reality with the new restrictions is that councils are being forced to turn overseas qualified professionals away.

"One of our clients had 11 candidates due to travel to the UK from the USA in the next few weeks to fill vacant child protection officer roles and now these are all on hold due to the visa situation.

"Both the council and the candidates are in limbo, the roles remain unfilled and existing employees struggle under the weight of increased case loads.

"We implore the Home Office to reconsider the restrictions put in place for the safety and wellbeing of children and families across the UK."

Home Secretary Theresa May announced in June that she was imposing a temporary limit on non-EU arrivals into Britain before a permanent cap is introduced next April.

The restrictions will mean 24,100 workers from outside Europe can enter the UK before April 2011 - a fall of 5% on last year.

A Government spokeswoman said: "Under the interim limit employers who urgently need to fill jobs in key shortage occupations, including children and families' social work, can seek additional permits.

"There is already a streamlined route to recruit overseas social workers working with children and families, as the profession is on the UK Border Agency's shortage occupation list.

"Ahead of introducing the permanent limit, we are consulting widely with employers and partners, including those in the social care sector, to ensure that their views and needs are taken into account."